1. Field of the Invention
The present invention relates to methods and apparatus for handling high peak pressures or shock waves in a firing chamber or gun barrel having a strength designed for a lower pressure or load and, more particularly, to arrangements for mitigating shock damage to a cartridge or casing containing explosive material when the explosive is detonated.
2. Description of the Related Art
When an explosive charge is detonated in a closed or restricted casing or cartridge, shock and/or pressure waves are produced which customarily cause an unreinforced case, container, or cavity to bulge, swell, stretch, or otherwise be deformed. This is because the shock wave from a detonation of high explosives typically induces an impulse to the cartridge that is beyond the elastic and plastic stress limits of conventional cartridge casing materials such as brass, aluminum or steel. Generally, the use of material to absorb the shock impulse prior to the shock wave hitting the cylindrical wall of the cartridge is impractical; small caliber cartridges in particular simply do not have enough volume to permit the inclusion of sufficient material to preclude deformation of the sidewall.
The strength of a cartridge case is tested most severely during firing. The pressure of the expanding gas imposes severe stresses on the cartridge case, and the case must be able to withstand the stresses without rupturing or being distorted to the extent that extraction of the case from the weapon is impeded. Another important factor in extraction, particularly in the case of automatic weapons having a high rate of fire, is elastic recovery of the cartridge case after firing. The case may be distorted for a brief time measured in small fractions of a second at the moment of burning or detonation of the charge. It is vital that the case recover from distortion to its original size very rapidly if the case is to be easily extracted from the chamber as soon as the cartridge is fired.
In conventional cartridge cases or containers, the chamber pressures are controlled by appropriate design of the reacting materials, the case or container, and the outer case, cavity or barrel. These designs are usually intended to provide a cartridge case which can be readily removed from the firing chamber after firing and replaced with another unit. This requires that no permanent deformation occur to the outer case, cavity, or barrel.
In certain outer cases, cavities, or barrels where peak design loads are low, maximum loads in the cases or containers used are accordingly limited. It would be an advance in the art of munitions and ordnance if there were a way to provide for a high-load output while using a relatively weak barrel. One particular solution to this problem is disclosed in application Ser. No. 07/265,747, now U.S. Pat. No. 4,986,186, entitled HIGH PEAK PRESSURE NOTCHED CARTRIDGE CASE, of LaRocca and Andersson, assigned to the assignee of the instant application.
The present invention involves a somewhat different approach by establishing a high-tension wrapping about the cartridge or casing to put the walls of the cartridge in compression, thereby pre-stressing the cylinder. Tee following patents are of interest in a consideration of this approach to the problem described above.
U.S. Pat. No. 2,792,324 of Daley et al discloses details of a particular procedure for winding resin impregnated yarn about a hollow container to provide a pressure vessel. Cylinders having a capacity of about 500 cubic inches were constructed which could withstand internal pressures of about 3000 pounds per square inch. Fiberglass yarn was preferred because of its high tensile strength and resistance to heat. A typical wall structure surrounding the container was composed of about 85% fiberglass and 15% insoluble resin.
U.S. Pat. No. 2,984,182 of Fienup et al discloses the formation of shot and shell tubes. This disclosure describes certain innovations introduced as departures from a conventional spiral winding technique.
U.S. Pat. Nos. 2,837,456 of Perilla, 3,706,256 of Grandy, and 4,738,202 of Hebert disclose various arrangements of composite ammunition cartridge cases in which a metal base is combined with a cylinder of resin impregnated filaments or filament reinforced plastic. Perilla and Grandy are concerned with developing a substitute for increasingly scarce strategic metals of that time, such as brass which was earlier preferred in the fabrication of artillery shell cartridge cases. Hebert discloses a design having a particular structural configuration which is directed to reducing excessive interface friction loads at the juncture between the cartridge base and cylindrical case.
U.S. Pat. No. 3,749,021 of Burgess discloses a metal-plated plastic cartridge case having a metal film between 0.05 and 0.1 mils thick plated onto a plastic cartridge case. This is done to increase the strength of the case and to improve its abrasion and burn-through resistance and its lubricity. Plastics are used in the cartridge cases of Burgess in place of brass, which is preferred, because of factors involving cost, weight and availability of the raw material.
U.S. Pat. No. 3,095,813 of Lipinski is directed to a propellant container for recoilless weapons. Lipinski discloses a container for use in a 120 mm. cartridge comprising a lamination of two resin-reinforced fiberglass layers with a plurality of helically wound wires between the layers. The wires are wound in a multiplicity of diamond-like patterns in order to promote a preferential break-up of the fiberglass cases. This arrangement is said to momentarily restrain the expansion of the propellant grains upon ignition in order to achieve the complete and efficient burning of the propellant, after which the container breaks up in preferred patterns for discharge through the venturi of the recoilless weapon.
It appears that none of these patents is directed to a solution of the particular problem addressed by the present invention.